When you get extra turns or dash actions, can you go faster?

The answer to the Amazing Lightspeed Horse exploit seems to indicate that no matter how many turns you get in a round (and thus no matter how many actions you get), you should only be allowed to move twice your speed after using at least one dash action, other dash actions being wasted.

Rogues get dash actions as bonus actions via ‘cunning action’, allowing them to potentially use two dash actions in a single round starting at level two. When I’ve played and GMed I’ve certainly allowed that to let people go thrice speed rather than double, for the same reasons explained in our question on that topic. Thieves also get an extra turn each first-round-of-combat at level 17, from Thief’s Reflexes, whose dashes I would also allow to move them up to their speed each, and who I would probably also have let move an extra set of movement for free.

This seems to contradict the highly upvoted and accepted answer claiming that no creature can ever for any reason use more than its speed in movement in a single round, though (except for a single dash action because ???).

Which interpretation is correct?